The requirements relating to the output and efficiency of internal combustion engines are become increasingly stringent. At the same time strict legal provisions require emissions to be kept at low levels. Such requirements can be easily satisfied, if the internal combustion engine is fitted with gas exchange valves and corresponding drives for these, with different valve lift characteristics as a function of the working point of the internal combustion engine. This allows throttle losses to be reduced as air is taken in and optionally allows high exhaust gas recirculation rates to be rapidly set.
It is known that the valve lift of a gas inlet valve in the internal combustion engine can be adjusted between a low and high valve lift. For example the Porsche 911 Turbo is fitted with a device for adjusting the valve lift of the gas inlet valve and the gas outlet valve. The internal combustion engine of the said vehicle is also provided with a camshaft, on which a cam with a low lift and two further cams with a higher lift are configured for each gas inlet valve. The cam lift is transmitted to the gas inlet valve by means of a transformer unit. The transformer unit is configured as a bucket tappet, comprising a cylinder element and an annular cylinder element disposed concentrically in relation to it. The cam with a low lift acts on the cylinder element, while the cams with the higher lift act on the annular cylinder element. As a function of the position of the bucket tappet, either the low or higher lift is transmitted to the gas inlet valve. During no-load operation of the internal combustion engine, the low cam lift is transmitted to the gas inlet valve. This results in reduced frictional losses due to the small diameter of the cam used in this operating state and the cylinder element and the lower valve lift.
A higher charge movement is also achieved. This enables the emissions of the internal combustion engine to be reduced and fuel consumption to be kept low at the same time. The low valve lift is maintained at low and medium load. If the load requirements imposed on the internal combustion engine are high, a switch is made to the higher valve lift.
If an intended switch of the valve lift actually fails to take place and this is not identified, it results in an increase in pollutant emissions in the respective cylinder during the combustion process.